Yes, there are some applications where down insulation is less than desirable (extreme damp, wet, or dirty), but the range of conditions under which down excels is increasing, thanks, in part, to innovative shell materials for sleeping bags and down clothing. Down lasts much longer, insulates better, and is far lighter than comparable synthetic insulation. New bag designs now bring down to the masses. Many premium manufacturers make down bags for all temperature ranges and conditions from -30 below to 60 above.
Contrary to the belief of some, Goose down is not feathers, but the soft, fluffy underlayer that insulates geese and other waterfowl against cold and wet conditions. Down is purchased by wholesalers and manufacturers as a commodity, much like agricultural products and natural fibers. Down comes in a variety of processing refinements which in addition to referring to the cleanliness and purity, denote the most important factor in evaluating down, the loft.

Kicking the Tires
Loft basically refers to volume. Greater volume means more trapped air, which in turn means warmer insulation. A quick ‘tire kick’ comparison between two bags of different insulation ratings can be done by simply observing the height of a bag when lying on a flat surface. The beefier volume, height, or general ‘fluff’ denotes a warmer, higher quality insulation. Technically speaking, loft is measured as volume per ounce and is a direct reflection of insulative power. Down used in most technical sleeping bags ranges from 550 Fill Power to 750+ Fill Power. A 550 down fill bag, utilizes insulation that occupies 550 cubic inches per ounce of down. A 750 Fill Power down occupies 200 more cubic inches of space per ounce!
The higher the loft number the more efficient the insulation, therefore the less of it needed to fill a similar size sleeping bag, in turn, the lighter the overall weight of the bag. Loft is also a reflection of the life expectancy of an insulation. Lower loft or fill power is susceptible to contamination sooner and may lose its functional loft (volume) earlier, compromising the performance of a technical sleeping bag.
Each manufacturer of down bags and clothing attaches a fill power rating to their insulation. Consumers need to choose bags carefully since each company utilizes this rating differently. A good mountain shop should be able to tell you how a particular manufacturer rates the quality of their down. The most reputable companies use independent testing agencies to rate each lot of insulation purchased, retesting the insulation at regular intervals, then arriving at a minimum fill power rating for their insulation.
A minimum fill power rating is the lowest tested power for any given batch of down. This differs from average and maximum fill power ratings, which are arrived at by utilizing a test average or maximum. Minimum fill power ratings ensure that the insulation in your bag is at least the stated insulation rating. More than one manufacturer of down products uses biased, internal ratings and even overstated fill powers by assigning maximums to a wide variance of down. In short, one manufacturers 750 fill power rating may be well under an audited figure of 700, while another manufacturers 750 may consistently rate above 800.
All of Backcountry Gear Ltd.’s down sleeping bags are independently tested for accurate fill power. Western Mountaineering and Marmot use minimum fill power ratings of 750 fill down for some of the highest loft, most efficient sleeping bags available.
Choosing the right down
Once you’ve narrowed your choice to a given temperature range (remember, your personal temperature needs may differ significantly from stated ranges), compare bags from different manufacturers by fill weight (measured in lbs/oz, this differs from total weight). If the bags are similarly sized, the heavier fill weight will indicate a more insulative, and therefore warmer bag (and higher quality too).
Other important criteria to consider in choosing down sleeping bags is the shell material. If you intend to use your bag where it may be exposed to frost, grime, dew, or other contaminants, be sure you choose a down bag with an appropriate technical shell fabric (a microfiber, Gore DryLoft, or another water/wind resistant breathable fabric). Some manufacturers now offer bags with sewn in wicking liners that prevent oils and dirt from contaminating the down, reducing the necessity of washing, extending the life of your bag, and adding several degrees of warmth. You may also buy these liners separately from specialty companies such as Design Salt.
To some, a down sleeping bag is the most thoroughly researched, and most cherished item in to occupy space in a gear closet. "Give it one night" they urge, "you’ll never go back."